Electrochemical storage devices play an important part of future energy strategy. Indeed, batteries are a viable energy storage technology of today and in the near future. A wide range of devices, such as portable electronic equipment, mobile household appliances, aerospace equipment, etc., are increasingly being powered by batteries. Accurate estimation of, for example, the state of charge of a battery can be difficult using known systems and methods. Thus, a need exists for systems, methods, and apparatus to address the shortfalls of present technology and to provide other new and innovative features.